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Transferring Green Power Between Grids

Using the latest advances in power grid technology, Burns & McDonnell is helping develop the TresAmigas SuperStation (TASS), the first power transmission hub to link the country's three primary electric grids and provide the smooth, reliable and efficient transfer of green power from region to region.

The superstation is planned on a 14,400-acre site near Clovis, N.M., in an area of some of the richest solar and wind renewable resources in the U.S. It will serve as a power exchange that facilitates the trading of electricity between interconnections. The exchange is being developed by Viridity and EPEX SPOT, a leading developer in European electric markets. Phase one of construction is scheduled to begin in summer 2012.

"This will be one of the most groundbreaking projects in power delivery in our generation," says Jeff Greig, vice president and general manager of the Burns & McDonnell Business & Technology Services Group.

The superstation will incorporate a network of high-voltage direct current (HVDC) voltage source converters that will transmit and balance power loads between the three electric network systems. This connection will allow electric systems stretching from coast to coast to operate together, optimizing the use of renewable energy. The superstation is designed to improve power reliability and assist with voltage and stability issues associated with the intermittent generation of renewable energy sources such as wind and solar in the interconnections, says Kiah Harris, Burns & McDonnell principal.

Unfortunately, this concentration of wind and solar energy is located at the edge of the three electric grid regions that aren't connected. The sparse population and resulting low electrical load in the area makes it only able to use to use a fraction of the renewable energy. The technology being used in the superstation allows the efficient large scale transfer of energy to the areas where demand is able to absorb it.

The expected 5,000 megawatt (MW) initial build out of the TASS will provide enough renewable energy to serve more than 2.5 million homes. Analyses of wind and solar generation in New Mexico, Texas and Oklahoma show significant generic growth opportunites for the TASS.

When power flows into the superstation, it is channeled through an HVDC voltage source converter (VSC) terminal. The facility looks like a huge, but typical, alternating current substation with extra buildings for the VSC electronics. High-voltage power electronics inside the converter switch electricity between alternating current (AC) and direct current (DC). "The VSCs are similar to plug-and-play building blocks," Harris says. "You can insert them as needed, increasing the transfer capability between grids."

Ongoing expansion plans for the TASS include underground pipelines of direct current superconductor cables. These cables can carry 5 gigawatts of electricity through a wire with a diameter 100 times smaller than can be done with copper conductors, without any losses.

"TresAmigas allows energy to flow between the interconnections where there may be market benefits on a massive scale," Harris says. "TASS will assist in the economic development of new renewable energy and transmission projects in the region."